Method of manufacturing an ultrathin optical element

ABSTRACT

The present invention provides an ultra-thin high-precision glass optic and method of manufacturing the same. The optic has an axial thickness that is less than 1,000 microns. A pattern and/or coating is disposed on a surface of the optic to provide attenuation of light in an optical system. In an embodiment, the optic is manufactured by disposing a pattern on a surface of a reticle. The pattern is covered with a first protective coating to protect the pattern. Individual optics are cut from the reticle so that each optic includes a portion of the pattern. The optic is thinned by removing material until it has an axial thickness of less than 1,000 microns. The optic is cleaned after thinning and covered with an anti-reflective coating.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/009,705 filed Dec. 13, 2004, which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The present invention relates to ultra-thin high-precision glass opticsfor use, for example, in photolithography tools, and methods ofmanufacturing ultra-thin high-precision glass optics.

BACKGROUND OF THE INVENTION

Photolithography systems/tools are used to print features on a substratein a variety of manufacturing applications. Typically, in operation, areticle having patterned features is exposed by an illumination sourcesuch as, for example, a laser to form images of the features. An opticalsystem projects images of the features onto the substrate.

Conventional photolithography systems control the amount of illuminationlight that reaches the substrate, for example, by light beam alignment,homogenizers, mechanical trimming, and/or diffractive elements. Theseconventional techniques disrupt the quality of light that reaches thesubstrate.

What is needed is a means for attenuating light in a photolithographysystem, as well as other optical systems, that does not disturb thequality of light.

SUMMARY OF THE INVENTION

The present invention provides an ultra-thin high-precision glass opticand method of manufacturing the same. It also provides an attenuationsystem that includes the ultra-thin high-precision glass optic, which isuseful for example in photolithography systems/tools.

The ultra-thin high-precision glass optic has an axial thickness that isless than 1,000 microns. A pattern and/or coating is disposed on asurface of the glass optic to provide controlled attenuation of lightintensity in an optical system. In one embodiment, the glass optic has apattern disposed on a first surface that attenuates light. An optionalanti-reflective coating covers the patterned surface and/or a secondparallel surface. In another embodiment, the glass optic has adielectric coating rather than the pattern on the first surface thatattenuates light. It is a feature of the glass optic that it minimizessecondary effects of aberrations, focal shift, black border effects,scattered light, et cetera.

The pattern comprises geometric shapes such as, for example, squares,dots, gratings et cetera that randomly or pseudo-randomly cover thesurface. The pattern can be formed, for example, using chrome.Alternatively, a dielectric coating can be used in place of the pattern.In embodiments, the pattern or dielectric coating attenuates incidentlight between five percent and twenty-five percent per unit area. Otherattenuation factors can also be achieved.

An optional anti-reflective coating covers the patterned surface and/ora second parallel surface through which light exits the glass optic. Thecoating improves light transmission through the glass optic by aboutfour to seven percent for each surface coated.

In an embodiment, the ultra-thin high-precision glass optic ismanufactured by disposing a pattern on a surface of an optical blank orreticle. The patterned surface is coated with a covering to protect thepattern and glass optic. Individual glass optics are cut from theoptical blank so that each optical element includes a portion of thepattern. The glass optic is thinned by removing material from the glassoptic until it has an axial thickness of less than 1,000 microns. Theglass optic is cleaned after thinning and coated with an optionalanti-reflective covering. During selected steps, wax may be used tofixture the optical blank and/or optical elements.

In a non-patterned embodiment, the ultra-thin high-precision glass opticis manufactured by coating a first surface of the optical blank orreticle with a protective covering. Individual glass optics are cut fromthe optical blank. The glass optic is thinned by removing material fromthe uncoated surface of the glass optic until it has an axial thicknessof less than 1,000 microns. The glass optic is cleaned after thinningand covered with a dielectric coating on the first surface. An optionalanti-reflective coating is applied to the surface through which lightexits the glass optic.

Further embodiments, features, and advantages of the present invention,as well as the structure and operation of the various embodiments of thepresent invention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 is a schematic diagram of a photolithography system that includesan attenuation system having ultra-thin high-precision glass optics.

FIGS. 2A-D are schematic diagrams of attenuation systems that illustratethe ultra-thin high-precision glass optics.

FIG. 3 is a schematic diagram of a single ultra-thin high-precisionglass optic.

FIG. 4 is a schematic diagram illustrating the light transmissionprofile of an ultra-thin high-precision glass optic.

FIG. 5 is a schematic diagram of an optional mask for an attenuationsystem having ultra-thin high-precision glass optics.

FIG. 6 is a flowchart of a method for manufacturing an ultra-thinhigh-precision glass optic.

FIGS. 7A-B illustrate a flowchart of a more detailed method formanufacturing an ultra-thin high-precision patterned glass optic.

The present invention will be described with reference to theaccompanying drawings. The drawing in which an element first appears istypically indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an ultra-thin high-precision glass opticand method of manufacturing the same. It also provides an attenuationsystem that includes the ultra-thin high-precision glass optic, which isuseful for example in photolithography systems/tools. While specificconfigurations and arrangements are discussed, it should be understoodthat this is done for illustrative purposes only. Persons skilled in theart(s) will recognize that other configurations and arrangements can beused without departing from the spirit and scope of the presentinvention. It will be apparent to persons skilled in the pertinentart(s) that this invention can be employed in a variety of otherapplications.

FIG. 1 is a schematic diagram of an example photolithography system 100that includes an attenuation system having ultra-thin high-precisionglass optics according to an embodiment of the present invention.Photolithography system 100 includes an illumination source 102,illumination optics 104, a pattern 106, projection optics 108, and asubstrate 110.

Illumination source 102 can be any source that emits light, includingultraviolet light. In an embodiment, illumination source 102 is a laser.Light emitted from illumination source 102 enters illumination optics104.

Illumination optics 104 condition the light emitted by illuminationsource 102. Various optical elements that can be used to condition lightsuch as, for example, diffusing optics, grating optics et cetera areknown in the relevant art(s).

Illumination optics 104 also include an attenuation system 105.Attenuation system 105 has multiple ultra-thin high-precision glassoptics that attenuate light without disturbing its quality. Attenuationsystems according to the present invention are described in more detailbelow with reference to FIGS. 2-5.

Pattern 106 is typically a reticle that has a chrome pattern disposed onit or a spatial light modulator that produces a pattern. In the case ofa reticle, light from illumination optics 104 passes through the reticleand reproduces the pattern disposed on the reticle on substrate 110. Inthe case of a spatial light modulator, light is reflected, for example,off of mirrors to produce a desired pattern on substrate 110.

Projection optics 108 focus the light from pattern 106 onto substrate110. In an embodiment, projection optics 108 also reduce the size ofpattern 106 in the process of focusing the light on substrate 110.

FIGS. 2A-D are schematic diagrams that illustrate various embodiments ofan attenuation system having ultra-thin high-precision glass optics.These embodiments can be used with photolithography system 100.

FIG. 2A is a schematic diagram of an attenuation system 200. Attenuationsystem 200 includes several ultra-thin high-precision glass optics 202that extend into a light path or light beam 204. Each of the ultra-thinhigh-precision glass optics 202 has an axial thickness that is less than1,000 microns. In embodiments, the axial thickness is on the order of0.500 mm, 0.300 mm, 0.200 mm, 0.150 mm, and 0.100 mm.

In one embodiment, a pattern is disposed on a surface 203 of each of theglass optics 202 to provide controlled attenuation of light passingthrough the glass optics 202. The amount of attenuation is determined bythe pattern. An optional anti-reflective coating covers the patternedsurface and/or the surface opposite the patterned surface through whichlight exits glass optic 202. In another embodiment, each glass optic 202has a dielectric coating on surface 203, rather than the pattern, thatattenuates light.

In the patterned embodiment, the pattern comprises geometric shapes suchas, for example, squares, dots, gratings et cetera that randomly orpseudo-randomly cover surface 203. The pattern can be formed, forexample, using chrome.

In an embodiment, each of the ultra-thin high-precision glass optics 202of attenuation system 200 is movable in the plane containing theultra-thin high-precision glass optics 202. The glass optics 202 aremoved, for example, using actuators (not shown) coupled to theultra-thin high-precision patterned coated glass optics 202. Byappropriately positioning of the ultra-thin high-precision patternedcoated glass optics 202, it is possible to optimize the uniformity ofthe light intensity that exposes substrate 110 without disturbing thelight quality.

The glass optics of attenuation system 200 can be oriented for exampleeither vertically, so that gravity acts perpendicular to the opticalaxis of each glass optic 202, or horizontally, so that gravity actsparallel to the optical axis of each glass optic 202.

More details regarding glass optics 202 are provided below withreference to FIGS. 3-4.

FIG. 2B is a schematic diagram of an attenuation system 210. Theultra-thin high-precision glass optics 202 of attenuation system 210 areseparated into two groups 202 a and 202 b. As shown in FIG. 2B, the twogroups 202 a and 202 b extend into light path 212 from oppositedirections. In an embodiment, each of the ultra-thin high-precisionglass optics 202 is movable in the plane containing the ultra-thinhigh-precision glass optics 202. The glass optics 202 can be movedeither closer to the center of light path 212 or closer to an edge oflight path 212 by actuators (not shown) coupled to the ultra-thinhigh-precision glass optics 202. In embodiments, attenuation system 210is installed, exchanged, replaced and/or relocated in photolithographysystem 100 as a unit or separately. This is also the case for the otherattenuation systems described herein.

FIG. 2C is a schematic diagram of an attenuation system 220 thatincludes ultra-thin high-precision glass optics 202 and an optional mask222. As shown in FIGS. 2C-D, the ultra-thin high-precision glass optics202 are separated into two groups 202 c and 202 d. Each of theultra-thin high-precision glass optics 202 that form a part of these twogroups is cantilevered into the light path.

In an embodiment, each of the ultra-thin high-precision glass optics 202of attenuation system 220 is movable in the plane containing theultra-thin high-precision coated glass optics 202. The glass optics 202can be moved either closer to the center of mask 204 or closer to anedge of mask 204, as illustrated in FIG. 2D, for example, either duringmounting or optionally by actuators (not shown) coupled to theultra-thin high-precision glass optics 202. By appropriately positioningof the glass optics 202, it is possible to optimize the uniformity ofthe light intensity that exposes substrate 110 without disturbing thelight quality. In embodiments, attenuation system 220 is installed,exchanged, replaced and/or repositioned in an optical system, such asphotolithography system 100, as a unit or separately.

FIG. 3 is a schematic diagram of a single ultra-thin high-precisionglass optic 202. As shown in FIG. 3, in an embodiment ultra-thinhigh-precision glass optic 202 has a length L, a width W, and athickness T. The length L is selected so that glass optic 202 issufficiently long enough to reach into an optical path of light to beattenuated. The width W is selected based on the frequency of light tobe corrected. In embodiments, W is on the order of 4 mm, 8 mm, and 12mm. The thickness T is less than 1,000 microns. In embodiments, T is onthe order of 0.500 mm, 0.300 mm, 0.200 mm, 0.150 mm, and 0.100 mm. Dueto the thinness of glass optic 202, ripples, shadows, and lightscattering effects are reduced. Other embodiments have differentdimensions and/or shapes.

In an embodiment, a short end 304 of ultra-thin high-precision glassoptic 202 is perpendicular to its long end 306, as shown for example inFIG. 3 and FIGS. 2A-B. In other embodiments, short end 304 is notperpendicular to long end 306, so that the glass optics 202 can beoriented at an angle as shown in FIG. 2D. Orienting the glass optics 202at an angle aids in controlling, for example, exposure of substrate 110due to any gaps between adjacent glass optics 202, particularly in astep-and-scan type photolithography tool.

A surface 302 of ultra-thin high-precision glass optic 202 has a patternor dielectric coating disposed on it that attenuates light. Inembodiments, the attenuation is between five percent and twenty-fivepercent. Other amounts of attenuation can also be achieved by varying,for example, the number of geometric shapes of the pattern on surface302 per unit area or the thickness of the dielectric coating on surface302.

In patterned embodiments, the pattern is typically composed of severalmillion geometrical shapes such as, for example, squares, dots, gratingset cetera randomly or pseudo-randomly (uniformly) distributed acrosssurface 302. The geometrical shapes can vary in size. In one embodiment,for example, the pattern is formed using small square chrome islandsapproximately 1.0-50 microns in size.

Ultra-thin high-precision patterned coated glass optic 202 is optionallycovered with an anti-reflective coating. In embodiments, theanti-reflective coating improves light transmission through glass optic202 by about four to seven percent for each surface coated (i.e.,coating both the surface where light enters glass optic 202 and thesurface where light exits glass optic 202 will improve lighttransmission by about eight to fourteen percent.).

FIG. 4 is a schematic diagram illustrating an example light transmissionprofile 402 for an embodiment of ultra-thin high-precision patternedcoated glass optic 202. In the embodiment shown, the transmission factorfor the entire length of ultra-thin high-precision patterned coatedglass optic 202 is 0.85. The amount of attenuation is thus fifteenpercent. The value 0.85 is only an example value, and it is not intendedto limit the present invention. Other embodiments of the presentinvention have other transmission profiles.

FIG. 5 is a schematic diagram of optional mask 222. Optional mask 222has a length L and a width W. The length and width of optional mask 222are selected, for example, based on the illumination cross sectionpresent at pattern 106 (or reticle) of photolithography system 100.

A surface of optional mask 222 is covered with several chrome lines 502.Chrome lines 502 reduce non-uniformities at substrate 110 that canresult from gaps between adjacent ultra-thin high-precision glass optics202. Chrome lines 502 are oriented at an angle θ with respect to an edgeof mask 222. The value of angle θ is selected to match the orientationof ultra-thin high-precision glass optics 202 (e.g., the chrome linesare positioned to block light passing between gaps in adjacent glassoptics 202). In an embodiment, the angle θ shown in FIG. 5 is equal tozero. In other embodiments, angle θ is greater than zero.

FIG. 6 is a flowchart of a method 600 for manufacturing an ultra-thinhigh-precision glass optic according to an embodiment of the presentinvention. Method 600 has six steps.

In step 602, a pattern is disposed on an optical blank. In anembodiment, the pattern is composed of several million geometricalshapes such as, for example, squares, dots, gratings et cetera randomlyor pseudo-randomly distributed across a surface of the optical blank.The sizes of the geometrical shapes can vary. In one embodiment, thepattern is formed using chrome and a conventional reticle manufacturingprocess. In embodiments, the number of geometric shapes of the patternper unit area is varied to achieve a desired transmission or attenuationfactor.

The optical blank can be any suitable glass optic such as, for example,commercially available reticles.

In step 604, the patterned side of the optical blank is covered with athin protective coating. The purpose of this coating is to protect thepattern and glass from small chips and other debris produced during step606. Any suitable coating that protects the pattern and glass, withoutharming it, can be used.

In step 606, the patterned optical blank is cut to form opticalelements. This cutting step can be performed using any known cuttingprocess such as, for example, saw cutting, machine grinding, handgrinding, milling, et cetera. Step 606 results in the production ofoptical elements having a desired shape and dimensions, except for axialthickness.

In step 608, the optical elements are thinned, for example, by grindingto a desired axial thickness of less than 1,000 microns. In embodiments,the optical elements are thinned for example to an axial thickness of0.500 mm, 0.300 mm, 0.200 mm, 0.150 mm, or 0.100 mm.

In step 610, the optical elements are cleaned. This cleaning steppreferably includes both mechanical cleaning and chemical cleaning. Thecleaning should not interfere with the patterns on the optical elementsand/or the glass surface.

In step 612, the optical elements are coated with an optional secondcoating. In embodiments, this optional coating is an optical coatingsuch as, for example, an anti-reflective coating. As used herein, anoptical coating refers to any coating intended to effect the opticalproperties of the optical elements. Optical coatings include, forexample, coatings that stop light reflections at the glass surface orthat block or facilitate the transmission of certain wavelengths oflight.

As will be understood by persons skilled in the relevant art(s), method600 can be used to manufacture optical elements that use a dielectriccoating, rather than a pattern, to attenuate light with certainmodifications. For example, when manufacturing optical elements that usea dielectric coating to attenuate light, step 602 is not performed. Thisis because such optical elements do not have a pattern. Whenmanufacturing such optical elements, the dielectric coating thatattenuates light is applied to the optical elements in step 612.

FIGS. 7A and 7B present a flowchart of a more detailed method 700 formanufacturing an ultra-thin high-precision optic according to anembodiment of the present invention. Method 700 has eight steps.

In step 702, a chrome pattern is disposed on a surface of a reticleblank. In an embodiment, the reticle blank is a commercially available6″×6″ reticle blank. The pattern is composed of several milliongeometrical shapes such as for example, squares, dots, gratings and/orother geometrical shapes randomly or pseudo-randomly distributed acrossthe surface of the reticle blank. In embodiments, the number ofgeometric shapes of the pattern per unit area is varied to achieve adesired transmission or attenuation factor. The pattern is formed usinga conventional reticle manufacturing processes.

In step 704, the patterned surface of the reticle blank is coated with aprotective covering. In one embodiment, the protective covering isphotoresist and enamel paint. Applying a thin 1 micron coating ofphotoresist (or enamel paint, optical tape, or wax) is typicallysufficient to protect the pattern and glass from small chips and otherdebris produced during cutting and grinding of the reticle blank. Theenamel paint is used to aid in fixturing the reticle blank in wax instep 706. Generally, wax will not stick to photoresist. Other coveringcan be used.

In step 706, the reticle blank is fixtured in wax. This is achieved bysinking the reticle blank in hot wax and allowing the wax to cool andharden.

In step 708, the reticle blank is saw cut, ground and/or milled to formseveral optical elements. These optical elements are formed to size,except for their axial thicknesses.

Depending on the setup and equipment used to cut and grind the reticleblank, the reticle blank and/or optical elements formed may have to beremoved from the wax, cleaned, and refixtured one or more times in step708 in order to properly size and finish each of the surfaces of theoptical elements.

After step 708, the optical elements are preferably checked to verifythey are within their required specifications prior to proceeding withstep 710. In an embodiment, specifications which can be checked includethe length, width, and end or side angles of the optical elements, plusoptical properties. Additionally, the parallelism of the sides of theoptical elements can be checked. Other specifications that can bechecked for other embodiments will become apparent to persons skilled inthe relevant art(s) given the description herein.

In step 710, the optical elements formed from the reticle blank arefixtured in wax for thinning. In an embodiment, several optical elementsare fixtured together in a wax having a higher than normal melting pointso that they can be thinned together in step 712. Fixturing multipleoptical elements together helps improve the stiffness of the fixturedstructure. The higher than normal melting point of the wax prevents theheat generated during thinning from softening and/or melting the wax.Thinning several optical elements together also helps ensure uniformity.

In step 712, the optical elements are thinned to a desired thickness.The optical elements are typically thinned to a thickness of 1,000microns or less by grinding and polishing. In embodiments, the opticalelements are thinned to a thickness on the order of 0.500 mm, 0.300 mm,0.200 mm, 0.150 mm, or 0.100 mm. During thinning, wax can be removedfrom between the optical elements, while leaving sufficient wax to holdthe optical elements, in order to facilitate polishing the opticalelements to a final desired thickness. A surface plate and laser rulerare preferably used to verify the thickness of the optical elements.

In step 714, the optical elements are cleaned. The optical elements arepreferably cleaned initially with diatomatious earth and a soapysolution such as Valtron while still fixtured. The optical elements arethen removed from the fixture and cleaned with toluene and acetone, orother commercial solvents, to dissolve the wax. At this point, one cancheck the optical elements for flatness using an interferometer. Theoptical elements are also cleaned using an acid bath to remove organicmaterials including the photoresist coating applied in step 704. Theoptical elements are also cleaned with methanol in preparation forcovering with an anti-reflective coat in step 716.

In step 716, the optical elements are coated with an anti-reflectivecoating. This coating improves the transmission of the optical elements.

In an embodiment, the optical elements are laid in a metal recess thatmatches the shape and thickness of the optical elements, and theanti-reflective coating is allowed to flow over the exposed surface ofthe optical elements. This process ensures a complete and uniformcovering of each optical element. If a recess is not used, or if thedepth of the recess does not match the thickness of the opticalelements, the ends of the optical elements may not be properly coated.

As noted herein, various specifications are checked to ensure theoptical elements perform as expected. The dimensions checked will dependon the shape and/or size of a particular optical element.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art(s) that various changes in form and detail can bemade therein without departing from the spirit and scope of theinvention. Thus, the breadth and scope of the present invention shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. A method, comprising: (a) forming a pattern on a surface of anoptical blank; (b) coating the pattern with a first protective covering;(c) cutting the optical blank, thereby forming an optical element thatincludes a portion of the pattern on a first surface of the opticalelement; (d) removing material from the optical element, thereby forminga second surface, until a thickness between the first surface and thesecond surface of the optical element is less than about 1,000 microns;and (e) coating the first surface of the optical element with a secondoptical covering.
 2. The method of claim 1, wherein step (a) comprisesrandomly forming a geometrical shape on the surface.
 3. The method ofclaim 1, wherein step (b) comprises forming chrome on the surface. 4.The method of claim 1, wherein step (b) comprises coating the patternwith photoresist.
 5. The method of claim 1, wherein step (c) comprisesgrinding an edge of the optical element.
 6. The method of claim 1,wherein step (d) comprises at least one of grinding and polishing the atleast one optical element.
 7. The method of claim 1, further comprisingbefore step (e) cleaning the optical element using at least one ofmechanically cleaning and chemically cleaning the optical element. 8.The method of claim 1, wherein step (e) comprises coating the firstsurface with an anti-reflective covering.
 9. The method of claim 1,wherein step (c) comprises forming a plurality of the optical element,wherein each of the plurality of the optical elements includes a portionof the pattern on a first surface of the respective optical element. 10.The method of claim 9, further comprising moving each respective one ofthe plurality of the optical elements individually in a plane containingthe optical elements.
 11. The method of claim 9, further comprisingmoving the plurality of the optical elements together as a unit.
 12. Amethod, comprising: (a) forming a pattern on a surface of an opticalblank; (b) forming a plurality of optical elements from the opticalblank, each respective one of the plurality of optical elementsincluding a portion of the pattern on a first surface of the opticalelements; and (c) removing material from each respective one of theoptical elements, thereby forming a second surface, until a thicknessbetween the first surface and the second surface of each respective oneof the optical elements is less than about 1,000 microns; wherein theplurality of optical elements move individually.
 13. The method of claim12, wherein step (a) further comprises forming a pattern of geometricshapes on the surface.
 14. The method of claim 12, wherein step (a)further comprises forming a pattern that attenuates light entering thesurface.
 15. The method of claim 12, further comprising positioning theplurality of optical elements such that at least one of the plurality ofoptical elements is movable in a plane normal to a thickness directionof the optical elements.
 16. A method, comprising: (a) forming a patternon a surface of an optical blank; (b) forming a plurality of opticalelements from the optical blank, each respective one of the plurality ofoptical elements including a portion of the pattern on a first surfaceof the optical elements; and (c) removing material from each respectiveone of the optical elements, thereby forming a second surface, until athickness between the first surface and the second surface of eachrespective one of the optical elements is less than about 1,000 microns;wherein the plurality of optical elements move as a unit.
 17. The methodof claim 16, wherein step (a) further comprises forming a pattern ofgeometric shapes on the surface.
 18. The method of claim 16, whereinstep (a) further comprises forming a pattern that attenuates lightentering the surface.
 19. The method of claim 16, further comprisingpositioning the plurality of optical elements, such that the pluralityof optical elements is movable in a plane normal to a thicknessdirection of the plurality of optical elements.
 20. A method,comprising: (a) forming a coating on a surface of an optical blank; (b)forming a plurality of optical elements from the optical blank, eachrespective one of the plurality of optical elements including a portionof the pattern on a first surface of the optical elements; and (c)removing material from each respective one of the optical elements,thereby forming a second surface, until a thickness between the firstsurface and the second surface of each respective one of the opticalelements is less than about 1,000 microns; wherein the plurality ofoptical elements move individually.
 21. The method of claim 20, furthercomprising positioning the plurality of optical elements, such that atleast one of the plurality of optical elements is movable in a planenormal to a thickness direction of the optical element.
 22. The methodof claim 20, wherein step (a) further comprises forming a dielectriccoating that attenuates light entering the surface.
 23. A method,comprising: (a) forming a coating on a surface of an optical blank; (b)forming a plurality of optical elements from the optical blank, eachrespective one of the plurality of optical elements including a portionof the pattern on a first surface of the optical elements; and (c)removing material from each respective one of the optical elements,thereby forming a second surface, until a thickness between the firstsurface and the second surface of each respective one of the opticalelements is less than about 1,000 microns; wherein the plurality ofoptical elements move as a unit.
 24. The method of claim 23, furthercomprising positioning the plurality of optical elements, such that theplurality of optical elements is movable in a plane normal to athickness direction of the plurality of optical elements.
 25. The methodof claim 23, wherein step (a) further comprises forming a dielectriccoating that attenuates light entering the surface.